PROJECT SUMMARY Young adult drinking is a public health issue. Current interventions yield small effect drinking reductions, thus, new approaches are needed. Smartphone applications (apps) have great potential for drinking moderation. Almost all young adults own a smartphone and most are open to technology use to moderate drinking. Though there are many moderate drinking apps, quality varies and there is no evidence any are more efficacious than a control condition for young adults. Thus, there is a knowledge gap as to which apps may be helpful. Brief interventions have shown personalized feedback based on motivational interviewing (M.I.) has efficacy, but these interventions give feedback about general patterns only, not drinking and impairment in the moment. Theory and evidence emphasize that slowing pace of drinking is difficult. These findings suggest young adults need additional help, preferably while drinking, to slow their pace of alcohol use. Apps have great potential for needed in-the-moment intervention. There are no efficacious, in-the-moment behavioral interventions for young drinkers. Human laboratory studies support perceived impairment as a focus of an in-the-moment, moderate drinking app. Two studies using different cognitive tasks (including a driving simulator) found heavier drinking young adults underrate impairment more than light drinkers. Simulated driving results in particular suggest serious consequences from misperceived impairment. An app that provides accurate feedback on impairment could increase perceived impairment and reduce drinking. This study will test an app providing in-the-moment feedback on impaired inhibitory control as an adjunct to an existing, M.I.-based, brief web-based intervention that gives feedback on overall drinking. App feedback will be tied to performance on the cued go/no-go task, which tests ability to respond quickly to ?go? targets (activation) while withholding responses to ?no-go? targets (inhibition). Moderate doses to blood alcohol content (BAC) .05-.06% reliably lead to inhibition errors, but higher doses are usually needed for ?go? reaction time (RT) to slow. Thus, ability to respond remains but ability to inhibit is impaired, which has negative implications. Using M.I.- consonant language, feedback will compare RT and inhibition failures after alcohol to RT and errors pre-drinking. The experimental app, which will be derived from a larger app in a current study, will be compared to 2 control conditions in which the task is completed without this novel feedback. Heavy drinking young adults (N=99) will be randomized to 1 of the 3 app conditions; dosed to BAC=.06% in small groups in a bar lab; then use the experimental or control app, followed by opportunity to self-administer more alcohol. Primary outcomes will be differences between study conditions on BAC and alcohol self-administered. During a 4-week period post-session, all participants will use the experimental app in actual drinking situations for 2 of the 4 weeks, enabling within-subject comparisons of drinking with vs. without the app. This study will yield preliminary data for an R01 to test concurrent use of multiple mobile tools (e.g., smartphone breathalyzer, wrist sensor) for combined efficacy in reducing drinking.